(i) Field of the Invention
This invention relates to an improved method for preparing 1,1-diphenyl-2-carboethoxycyclopropane and certain related substituted phenyl compounds. More particularly it relates to the reaction of 1,1-diphenylethylene with ethyl diazoacetate without using a metal catalyst.
(ii) Related Art
The compound 1,1-diphenyl-2-carboethoxycyclopropane (hereinafter DPCCP) has utility as an intermediate in the preparation of pharmaceuticals and other products. For example, see "Cyclopropanes and Cyclobutanes LXXII. Reactions of 1-Phenyl-2-Aminocyclopropanes with Alcohols" by Levina, R. Ya. et al. in Zh. Org. Khim. (1977) Vol 13, Issue 3, at pages 543-7 (hereinafter Levina). Levina discloses that the precursor DPCCP (ethyl 1,1-diphenyl-2-cyclopropanecarboxylate) was synthesized as Compound VII from 1,1-diphenylethylene and diazoacetic ester. The yield was 40%; bp 182.degree.-185.degree. C. (5 mm Hg). Levina refers to "Reference 9" for the method of preparation. Reference 9 is a Dissertation by A. S. Koz'min, Moscow State University (1971). The Lenin Library in Moscow was asked to sell a copy of Reference 9 but responded that it is "unavailable". A computer search indicated that Chemical Abstracts Service had not indexed any "Dissertation" by Koz'min. Accordingly "Reference 9" does not appear to be prior art.
A number of references describe the preparation of DPCCP from 1,1-diphenylethylene (hereinafter DPE) and ethyl diazoacetate (hereinafter EDZC). However, they all apparently relate to the use of a metal catalyst. For example, see "Enantioselective Synthesis of 2-Phenylcyclopropanecarboxylates through Chiral Cobalt Chelate Complex-Catalysed Carbenoid Reactions" by Tatsuno et al., J. C. S. Chem. Comm. (1974) at pages 588-589 (hereinafter Tatsuno). The reactions were all apparently carried out at 10.degree. (sic) with different types of cobalt-based catalysts. Some of the cobalt catalyst systems gave optically active products; other cobalt catalyst systems gave products that were totally optically inactive or slightly active.
Essentially, nowhere does the now-known prior art disclose the use of either (1) absence of catalyst; or (2) high temperatures.